Add fiat denomination to send and receive inputs

[design-rrr]

Atm only sats and BTC are available, having the option input the value in fiat would be useful for end-users.
The available currency in the buttons should be relative to fiat denomination selected in preferences.

[shocknet-justin]

This could be a little tricky since the user expectation may be that the invoice is dynamic to the fiat rate.

We do show the approximate fiat value for quick estimation when creating an invoice.

What's the intent for using fiat at this input vs. a fiat denominated clink offer or pay link?

[design-rrr]

Fiat would only define the amount in sats. Most merchants still defiling prices in fiat currencies and instead of generating invoices, simply have a static QR with the LNaddress. The customer in this case need to insert the amount in fiat to pay the merchant

[shocknet-justin]

The customer in this case need to insert the amount in fiat to pay the merchant

The customer can't supply a fiat amount for a fixed-fiat-priced product because there will always mismatch between their quote and the quote the merchant is using to generate the invoice, even if only by a few sats. Since the invoice is generated on the receiving it's from there that the exchange rate must be supplied, and informational only for the user so they can accept/decline to pay the invoice.

Spontaneous payments where the payer wants to send a fiat amount is where this could be done, from the send screen.

Dynamically updating would have to be done at the offer level so that Pub can always generate the next invoice based on exchange rate, ad-hoc invoices however would only generate once and exchange rates change tick by tick, which can drift before expiration.